Ionic pump



United States Patent O 3,172,597 IGNIC PUMP Lucien Guyot, Paris, France,assignor to Compagnie Francaise Thomson-Houston, Paris, France FiledJuly 5, 1961, Ser. No. 122,067 Claims priority, application France,.luly 8, 1960, 832,470 8 Claims. (Cl. 23u- 69) The present inventionrelates to an ionic pump of the getter type with a self-actuateddischarge in a magnetic field and having the advantages of negligibleouter magnetic field, reduced size and very light weight.

It is known that in certain ionic pumps of the getter type, such asthose described in U.S. Patent No. 2,755,014 filed April 24, 1953, anautonomous ionic discharge known as the Penning discharge is used, saiddischarge being produced in non-parallel electrical and magnetic fields.According to a preferred embodiment, the ionization chamber of such apump contains a positive electrode in the shape of a hollow cylinder andtwo negative electrodes made of a material, such as titanium or carbonwhich absorbs gaseous ions. These two electrodes are oppositely arrangedat the open ends of the positive electrode. This system is located in amagnetic field parallel to the axis of the cylinder and produced by amagnet arranged outside the enclosed space containing the system. Whenan ionic discharge takes place between these electrodes, the electronsproduced can only reach the positive electrode along very long helicalpaths. Thus the likelihood of ionizing shocks is increased to the pointat which the discharge is maintained at extremely low pressures. Theions produced travel towards the negative electrodes which absorb them.

These pumps, which require no other means of operation than a highvoltage supply, are very suitable to remain sealed permanently toelectronic tubes in which it is desired to maintain a high vacuum.However, up to now they could not be associated with tubes usingprecision electron optical systems, and more particularly those in whichlow speed electrons are encountered, such as camera tubes and imagetubes. In fact, these pumps have a considerable outer magnetic eld whichintroduces intolerable defects into the electron optics. In principle itis possible to have an effective magnetic screening either of the pumpor of the electronic tube, but this increases the volume and the Weightof the assembly to a prohibitive extent, in particular in the veryfrequent cases in which the electronic tube is fragile and in whichfurthermore it must operate in transportable devices.

The present invention has for an object to provide an ionic pump of thegetter type with a magnetic field which, whilst having a small volumeand -a light weight, has hardly any outer magnetic lield. The principleof the invention consists in reducing the outer eld by means of acompensating magnetic structure.

The present invention provides an ionic pump of the getter type using anionization chamber, in which there prevails a magnetic field, having thefollowing arrangements:

The ionization chamber is essentially constituted by a hollow cylinderof a non-ferromagnetic material connected on either side toferromagnetic plates. It is surrounded by a magnet in the shape of ahollow cylinder magnetized in the direction of its axis and magneticallyconnected to the two ferromagnetic plates. Outside the chamber andcoaxial with it, is arranged a second magnet, a so-called compensationmagnet, preferably of identical shape to the first, magnetized in theopposite direction to that of the first and magnetically connected byone of its polar faces to one of the two plates of the chamber and bythe other to a third ferromagnetic plate.

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According to a preferred embodiment, the assembly is surrounded by amagnetic screen in the form of `a box, two opposite walls of which aremagnetically connected respectively to the two end plates of theassembly, each of the plates being capable of constituting one of thewalls of the box.

The term magnetically connected, as applied to these elements of themagnet circuit indicates, according to common usage, any arrangement forwhich the reluctance between these elements is very small in relation tothe total reluctance of lthe circuit. The magnetically connectedelements can therefore be either in immediate contact, or integral withone another, but may also be separated by a fairly narrow gap orconnected by means of a third ferromagnetic element.

The invention will now be further described with reference to theaccompanying drawings, in which:

FIGURE 1 illustrates a non-compensated structure,

FIGURE 2 illustrates the principle according to this invention,

FIGURE 3 illustrates one construction of ionic pump according to thisinvention, and

FIGURE 4 illustrates an embodiment comprising two ionic pumps.

The pump which is the object of the invention, even in its most simpleform, i.e. without screening, has a very small leakage eld. In fact, itsmagnetic structure is approximately symmetrical in relation to a plane.The external fields produced by each half thus practically compensatefor each other at a certain distance from the structure. For thisreason, lthe screening which is used in the preferred embodiment canhave reduced dimensions and its walls can be thin.

Another advantage of this pump arises from the fact that thecompensation magnet, while weakening the leakage eld, reinforces theield in the useful area of the pump. This effect will be illustrated byFIGURES 1 and 2, wherein FIGURE 1 diagrammatically shows the inductionspectrum for a non-compensated structure and FIGURE 2 shows that foundin a structure according to the invention. It may be seen that in thefirst case the magnetV 1 produces a ux the parasitic component of which,corresponding to the induction lines 2, is comparable to the usefulcomponent 3. This latter stems from the large extent of the polar faces,one of which is constituted by one whole side of the plate 4 and theother by the inner surface of the screening box 5 connected to the plate6.

This is no longer the case in the structure according to the inventionand diagrammatically shown in FIG- URE 2. In this iigure, a secondmagnet 7 magnetized in the opposite direction to that of 1, is connectedon the one hand to the outer surface of the plate 4 andon the other handto an inner surface of the screening box 5. The parasitic flux is veryreduced because the para- -sitic induction lines can only originate inthe half situated towards the magnet 1 of the circumferential zone ofthe plate 4. In fact no induction line produced by the magnet 1 can passthrough the plane of symmetry 9 of the structure. The lessening in theparasitic flux results in an advantageous reinforcement of the usefulinduction, allowing the volume of the pump to be reduced and thusfacilitating its use on fragile electronic tubes.

The invention preferably applies to the ionic pumps of the type shown inU.S. Patent No. 2,755,014. In this case each of the two ferromagneticplates supports an electrode made of a material which absorbs the ionsof the gas to be pumped whilst a third electrode of annular shape takento a positive potential in relation to the two previous ones is arrangedin the space between the latter coaxially in relation to the lineconnecting them.

Ving into the chamber 1.

surface of the plate 14.

But the invention is not limited to these types of pumps and it may beapplied to any system of ionic absorption pumpsythe ionization chamberoffwhich is subjected to a magnetic field.

FIGUREy 3-diagrammatically shows an embodiment ofthe ionic pump which isthe object of the invention.

The pump in FIGURE 3 is made-up of a discharge structure contained in anionization chamber-10 vand of an outer structure 11 co-operating withthe members of the chamber 16 in order to create a magnetic fieldlimited to the chamber' 10. This chamber-is constituted by a glasscylinder 12 sealed to two-plates 13,v 14 of ferromagnetic material, forexample rKovar. The plateV 13, which has a greater diameter than 14,comprises a gas inlet port 15. A glass pipe 16 `sealed tothe plate 13connects the pump to the electronic tube to be pumped. These plates 13and 14 have projections 17, 18' extend- The projections 17, 18 arecovered with sheets 19, 20 of a material such as carbon or titaniumwhich can absorb the gases in fthe ionized state. These sheets areintended toconstitute the negative electrodes of a Penning discharge,the positivey electrode being constituted -byV a hollow cylinder 21arranged the walls 27 comprises an opening into which islocated theplate 13, whilst-the opposite wall 28 comes into contact with the magnet25. Finally the cylindrical 'members 29, 30 of ferromagneticmateriaL-similar to the members 17, 18 are fixedwithin the axis of thestructure on to the inner surface-ofthe Wall 28 and on to the outer Inthis 'pump'the plate 14 is magnetically connected to the polar facesofthe two mag- Ynets 23 and 25 by means of the ferromagnetic ring 24,

and the wall 28 of the box 26 forms the ferromagnetic plate connected,according -to-the invention, to the lend of the compensation magnet 25.The induction fiuxoband the two adjacent ferromagnetic platesat-:itsends can enclose the ionization chamber f a second pumpcooperating with'the first.

(b) In pumps containing-a single yactive structure, the compensationmagnet can be constituted by a solid cylinder arranged on the axisoffthe pump.

(c) The discharge electrode orelectrodes of the pump can be directlyvfed `bythe current conductors `of the velectronic tube to be pumped, theconnecting conductor being inside the vacuum enclosure.

FIGURE 4- fshows an embodiment comprising two ionic pumps 4and vhavingtwo ionizationrchambere'as `described in paragraph (a) above.

Certain elements of this latter embodiment, referenced 16 to 30, havesubstantially the same functions as those elementsbearing the numberscorresponding references in FIGURE 3. In addition, the embodiment of FG-URE 4 comprises the following parts:

A second glass cylinder 31, constituting with the elements 12, 13, 14,28 the vacuum-tight enclosure.

A second hollow cylinder 32 constituting `the positive electrode of thesecond ionization chamber.

An electrical conductor 33 connecting the electrode 32 to the electrode21 through an aperture 34 in the ferromagnetic plate 14.

Sheets 35 and 37 of a material absorbing gases in the ionized state,just like the sheets 19 and 20. These sheets 36 randy 37 cover theferromagnetic cylindrical elements and constitute the negativeelectrodes of the second ionization chamber.

It is clear that for constructional reasons the casing 26 cannot form asingle part with the plate 2S, as is .the

vcase in FIGURE 3, but these two elements are magnetically connected ashereinbefore explained. TheV plate 23 is separated from the box 26 bythe spacing shown at 35. The magnetic 'connection between the plate 28and the magnet 25 is therefore ensured.

I claim:

1. An ionic pump of the getter type having an ionization space which issubjected to a magnetic field, comprising a hollow cylinder ofnon-ferromagnetic material defining the ionization space, a firstferromagnetic member arranged at one end of the hollow cylinder, asecond .ferromagnetic member arranged at the other end of said hollowcylinder, at least one of .said ferromagnetic members supporting anelectrode of ion absorbing `material on its surfacefacing the interiorof the hollow cylinder, an annular Velectrode within the hollow cylinderarranged between the rfirst and the second ferromagnetic members andhaving'its open ends directed towards these members and adapted to becarried to a positive potential with respect to these members, anaperture in one of said ferromagnetic members forming an inlet for thegas to be pumped, a supply conductor to said annular electrodeextendingthrough said aperture, a first magnet in the form of a hollowcylinder magnetized in the axial direction which surrounds vsaid hollowcylinder and is magnetically connected tothe rst and the Vsecondferromagnetic members, a second magnet arranged Aoutside the assemblyformed by said first magnet and the first and the second ferromagneticmembers coaxially therewith and acting as a compensation magnet which ismagnetically connected by one of its polar faces to the secondferromagnetic member and magnetized in the opposite direction to kthe.first magnet, and a third ferromagnetic member magnetically connectedto the Vother polar face of the second magnet.

2. A pump as claimed in claim 1, comprising a surrounding magneticscreening structure in the form of a box magnetically connected to thefirst and third ferromagnetic members.

3.'A pump as claimed in claim 2 in whichthe third ferromagnetic memberconstitutes one of the walls `of the box.

4. Apump as claimed in claim 1, including a second ionic pump .structureco-operating with the first ionic pump and arranged between the second.and third ferromagnetic members, said second pump structure alsocomprising a hollow cylinder of non-ferromagnetic material defining theionization space and extending between said second and thirdferromagnetic members, an electrode of ion absorbing material supportedby at least one of said second and third ferromagnetic members andfacing the interior ofthe. hollow cylinder, an annular electrode withinthe hollow cylinder having its ends directed towards said second andthird ferromagnetic members, ,an `aperture in said second ferromagneticmember forming an inlet for the gas to be pumped and providingcommunica- `tion between the ionizationspaces of the two pumps, a

supply conductor for connecting said annular electrode to a positivepotential extending through said aperture and connecting with the supplyconductor to the annular electrode of the first pump, and said secondpump structure being surrounded by said second magnet.

5. A pump as claimed in claim 1, in which the second magnet is similarto the first magnet.

6. A pump as claimed in claim l, in which the second magnet isconstituted by a hollow cylinder.

7. In an ionic pump comprising a member of nonferromagnetic materialdefining an ionisation chamber containing members of ion absorbingmaterial and surrounded by a magnet structure producing a magnetic fielddirected axially of the chamber, the improvement which comprisesarranging compensating magnet means which are magnetized in the oppositedirection to the magnet structure externally of said chamber in order toreduce the magnetic lield produced outside said chamber.

8. In an ionic pump comprising a member of nonierromagnetic materialdefining an ionisation chamber containing two spaced members of ionabsorbing material and an annular electrode arranged between said twomembers which is adapted to be carried to a positive potential andwherein a magnet structure is arranged around said chamber to produce amagnetic lield extending axially of said chamber and said annularelectrode, the improvement which comprises arranging compensating magnetmeans which are magnetised in the opposite direction to said magnetstructure externally of said chamber in order to substantially reducethe magnetic field produced outside said chamber.

References Cited in the le of this patent UNITED STATES PATENTS

1. AN IONIC PUMP OF THE GETTER TYPE HAVING AN IONIZATION SPACE WHICH ISSUBJECTED TO A MAGNETIC FIELD, COMPRISING A HOLLOW CYLINDER OFNON-FERROMAGNETIC MATERIAL DEFINING THE IONIZATION SPACE, A FIRSTFERROMAGNETIC MEMBER ARRANGED AT ONE OF THE HOLLOW CYLINDER, A SECONDFERROMAGNETIC MEMBER ARRANGED AT THE OTHER END OF SAID HOLLOW CYLINDER,AT LEAST ONE OF SAID FERROMAGNETIC MEMBERS SUPPORTING AN ELECTRODE OFION ABSORBING MATERIAL ON ITS SURFACE FACING THE INTERIOR OF THE HOLLOWCYLINDER, AN ANNULAR ELECTRODE WITHIN THE HOLLOW CYLINDER ARRANGEDBETWEEN THE FIRST AND THE SECOND FERROMAGNETIC MEMBERS AND HAVING ITSOPEN ENDS DIRECTED TOWARDS THESE MEMBERS AND ADAPTED TO BE CARRIED TO APOSITIVE POTENTIAL WITH RESPECT TO THESE MEMBERS, AN APERTURE IN ONE OFSAID FERROMAGNETIC MEMBERS FORMING AN INLET FOR THE GAS TO BE PUMPED, ASUPPLY CONDUCTOR TO SAID ANNULAR ELEC-